Many different types of electrical converters make use of press pack modules for their easiness to bring them into series connection with the help of a mechanical stack, where more than one module is provided in series. Press pack modules are made to be mounted in between cooler or pressure plates and pressure is applied to that stack to ensure proper electrical and thermal contact between the individual press pack modules. For HVDC converters, up to 20 modules can be put in series connection into one stack and more than a hundred stacks can be needed for the complete converter. This means that a large number of heavy and sometime expensive mechanical parts are needed to create those stacks.
An example of a prior art press pack stack is disclosed in FIG. 1. As seen in this figure, a standard stack comprises two or more rods, equally spread around the stack. Two yokes are provided, one at each end of the stack, to enclose the stack. Furthermore, a spring packet is provided on the top of the stack to provide a pressure thereon. In some press stack packs this spring packet is omitted and instead special yokes are provided which allow the use of their inherent mechanical elasticity as spring force.
Another example of a press pack stack is disclosed in the U.S. patent application publication US2010/0133676 A1.